For instance, the energy exchange system is an energy storage system. Energy storage systems play an important role in an improvement of a stability of power supply networks. Sensible thermal exchange systems are state of the art for storing fluctuating energy from renewable sources.
Electrical excess energy from a main supply grid is transformed into heat (thermal energy) and is stored in heat storage material of a heat exchange chamber of the heat exchange system.
In times with no or low occurrence of wind, the stored thermal energy is used for generating steam to produce electrical energy over a steam turbo generator and the produced electricity is fed in the main supply grid.
Sensible energy storage can be realized for example by heating up a solid thermal storage material like stones or gravel. The material is heated up and kept at high temperature levels over a long period of time.
Storing large amounts of energy for grid balancing requires large quantities of solid storage material with a heat capacity in the magnitude of 1 kJ/kg K.
The storage material needs to be founded on the ground. Therefore, the soil is heated up by through an insulation to the ground. Heat is transferred to the soil. This leads to two areas of problems. The first being a legal problem: it is generally not allowed to heat the groundwater more than a couple of degree Kelvin in Germany. The second being a design problem: materials have to be suitable to the prevailing temperature.
State of the art is thermal insulation and use of temperature resistant materials for sensible heat storages. This is possible since most of the state of the art sensible heat storages do not hold very high temperature levels, whereas heat storages used in combination with a conventional steam cycle need to store heat at very high temperatures. Alternatively, the storage can be cooled down completely after every single cycle. This leads to high losses of energy since low temperature heat cannot be recycled (in a closed loop) in the following charging cycle.